The most recent research on blood vitamin D status and cancer survival suggests that vitamin D adequacy reduces the risk of death in breast, colorectal, lung, and prostate cancer, leukemia and lymphomas, and all cancers combined.1 Research on vitamin D supplementation, summarized in a 2014 Cochrane analysis, found that supplementation with vitamin D3 was associated with reduced risk of cancer mortality.2

The idea that vitamin D could protect against cancers arose in 1980; based on an earlier observation that colon cancer mortality was the highest in geographical areas exposed to the least amounts of sunlight.3,4 Several more studies of geographical variations in cancers have since found the same result: inverse relationships exist between sun exposure and 24 types of cancer, including the most common cancers – those of the breast, colon, rectum, and prostate.5,7 Because most people’s primary vitamin D source is sunlight, vitamin D insufficiency is thought to be one reason for the cancer survival disparities that exist between African Americans and white Americans (darker skin is less efficient at producing vitamin D in response to UV rays).1

Since 1980, evidence for the involvement of vitamin D in the relationship between sun exposure and decreased cancer risk has progressively accumulated, as associations were found between blood vitamin D levels and reduced risk of cancers.8,9 Further support for the importance of vitamin D in cancer prevention was provided by randomized controlled trials of vitamin D supplementation that showed reduced cancer risk compared to placebo. There have also been many reports that vitamin D receptor gene mutations, which interfere with the normal biological actions of vitamin D, were associated with increased cancer risk.10-12

Additional studies confirmed that vitamin D has growth-inhibitory effects on cells derived from breast, colon, prostate, and skin cancers.13 Vitamin D can block cancer cell growth in a number of ways: Vitamin D alters the expression of genes that regulate inflammation, cell death and cell proliferation, and also interferes with the growth-promoting actions of IGF-1 and other growth factors. Additional anti-cancer effects of vitamin D include enhanced DNA repair and immune defenses, and angiogenesis inhibition.14,15

Today, over 800 scientific papers have been published on the relationship between vitamin D and cancers. We now have ample evidence that maintaining adequate vitamin D levels is an effective strategy for protection against cancer.

Considering all of this evidence, achieving vitamin D sufficiency is so very important. Unfortunately, the Institute of Medicine is hesitant to significantly raise its vitamin D recommendations, so most multivitamins still do not contain nearly enough vitamin D (only 400 IU) to offer the security that a normal Vitamin D level will be achieved. In my experience, 2000 IU has been an appropriate dose to bring most people into the favorable blood 25(OH)D range of 30-45 ng/ml (I also recommend getting a blood test to confirm adequate levels). I also recommend avoiding multivitamin supplements that contain folic acid, beta-carotene, copper, and vitamin A; these are potentially harmful ingredients. To learn more about choosing a multivitamin, read these articles:If I eat a healthy diet, do I really need a multivitamin?Multivitamins: Ingredients to Avoid